Method for manufacturing substrate for semiconductor light emitting element and semiconductor light emitting element using the same

ABSTRACT

A light emitting element having a recess-protrusion structure on a substrate is provided. A semiconductor light emitting element  100  has a light emitting structure of a semiconductor  20  on a first main surface of a substrate  10 . The first main surface of the substrate  10  has substrate protrusion portion  11 , the bottom surface  14  of each protrusion is wider than the top surface  13  thereof in a cross-section, or the top surface  13  is included in the bottom surface  14  in a top view of the substrate. The bottom surface  14  has an approximately polygonal shape, and the top surface  13  has an approximately circular or polygonal shape with more sides than that of the bottom surface  14.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a 37 C.F.R. §1.53(b) divisional of U.S.application Ser. No. 12/004,079 filed Dec. 20, 2007 now U.S. Pat. No.7,781,790, which in turn claims priority on Japanese Application No.2006-344482 filed Dec. 21, 2006 and Japanese Application No. 2007-271764filed Oct. 18, 2007. The entire contents of each of these applicationsare hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a semiconductor device having a recessor protrusion (hereinafter may be referred to as recess/protrusion)provided on a substrate and, more particularly, to a semiconductor lightemitting element that improves its external quantum efficiency by havingthe recess or protrusion provided on the substrate, and a substrate usedtherein and a method of manufacturing them.

2. Background Art

A semiconductor element, i.e., a light emitting diode (LED) basicallycomprises an n-type semiconductor layer, an active layer and a p-typesemiconductor layer stacked on a substrate in this order, and electrodesare formed thereon. Light from the active layer is discharged outside ofthe element from such as outwardly exposed surfaces (top surface, sidesurface) of the semiconductor structure and exposed surfaces (backsurface, side surface) of the substrate.

In detail, when light generated in the semiconductor layer enters aninterface with an angle of incidence not smaller than the critical anglewith respect to the interfaces with the electrodes or the interface withthe substrate, the light laterally propagates while repeating totalreflection within the semiconductor layer.A part of light is absorbed during the propagation, resulting in lowerexternal quantum efficiency.

A method of roughing the top surface and side surfaces of the lightemitting diode chip has been proposed, but it may cause damage on thesemiconductor layer and results in cracks and/or other trouble. Thisleads to partial breakage of p-n junction and reduction in internalquantum efficiency.

Accordingly, provision of recess/protrusion on a surface of a substrateof a semiconductor growing side has been considered.

Methods for providing the recess/protrusion on a growth surface of asubstrate have been described in literatures below. With reference toPatent Literature 3 are: Japanese Laid Open Patent Publication Nos.2006-066442, 2005-064492, 2005-101230, 2005-136106, and 2005-314121; andwith reference to Patent Literatures 4 and 5 are: Japanese Laid OpenPatent Publication Nos. 2000-331937, 2002-280609, and 2002-289540.

-   Patent Literature 1: Japanese Laid Open Patent Publication No.    2003-318441,-   Patent Literature 2: Japanese Laid Open Patent Publication No.    2005-101566-   Patent Literature 3: Japanese Laid Open Patent Publication No.    2005-047718-   Patent Literature 4: Japanese Laid Open Patent Publication No.    2002-164296-   Patent Literature 5: Japanese Laid Open Patent Publication No.    2002-280611-   Patent Literature 6: Japanese Laid Open Patent Publication No.    2001-053012

Each of the patent literatures 1-6 discloses provision of therecess/protrusion on the growth surface of the substrate. PatentLiterature 3 and the above-described reference literatures describeprovision of an etch pit in the sapphire substrate by wet etching usingphosphoric acid.

When an optical structure having light extracting feature is provided onthe semiconductor structure side of the substrate surface thecrystallinity of the semiconductor grown thereon may be degraded due tothe recess/protrusion configuration, because the surface also functionsas a crystal growth surface. In addition, if a void is present in therecess provided in the substrate, light extraction efficiency may bedecreased. Also, even if the substrate surface has a structure capableof improving the light extraction efficiency, the directionalcharacteristics of emission may be adversely affected.

SUMMARY OF THE INVENTION

The present invention provides a substrate for a light emitting elementand light emitting element which are excellent in crystallinity andlight extraction efficiency, and a method of manufacturing them.

A semiconductor light emitting element according to an embodiment of thepresent invention has a semiconductor light emitting structure on afirst main surface of a substrate. A protrusion portion is provided onthe first main surface of the substrate. A protrusion has a shape inwhich the bottom surface is wider than the top surface in its crosssection or the bottom surface includes the top surface in the top viewof the substrate, the bottom surface has an approximately polygonalshape, and the top surface has an approximately circular or polygonalshape having constituent sides (hereinafter may be referred to as“sides”) more than that of the bottom surface.

In another embodiment according to the above-described embodiment, (1)each side surface of a protrusion is formed with a complex surfacecomprising more surfaces than that of the number of constituent sides ofthe approximately polygonal bottom surface.

A semiconductor light emitting element according to an embodiment of thepresent invention has a semiconductor light emitting structure on afirst main surface of a substrate. A protrusion portion is provided onthe first main surface of the substrate. A protrusion has a shape inwhich the bottom surface is wider than the top surface in its crosssection or the bottom surface includes the top surface in the top viewof the substrate, the shape of the bottom surface is approximatelypolygonal, the top surface is approximately polygonal having the numberof constituent sides the same or less than that of the bottom surface,and a side surface of the protrusion is formed with a complex surfacemade with more surfaces than the number of constituent sides of theapproximately polygonal bottom surface.

In other embodiments according to each of the above-describedembodiments, (1) In the first main surface, the substrate protrusionportion includes a plurality of protrusions that are spaced apart eachother. (2) In the first main surface of the substrate, the protrusionsare arranged periodically. (3) the periodic arrangement of theprotrusions is triangular, quadrangular, or hexagonal lattice, and (4)the shape of the bottom surface is approximately triangular.

A method of manufacturing a semiconductor light emitting elementaccording to an embodiment of the present invention comprises a processof providing a mask on a first main surface of a substrate, a process offorming a recess/protrusion structure on the substrate in which aplurality of protrusions having different shapes at the top surface andthe bottom surface are formed spaced apart from each other by etchingthe substrate through the mask, and a process of forming a semiconductorsubstrate by growing a semiconductor on the surface of the protrusionsor recesses of the substrate.

Other embodiments according to the embodiments described above include:(1) the process of providing a mask at least includes processes ofproviding a first mask which defines the shape of the bottom surface ofprotrusions and providing a second mask which defines the shape of thetop surface of the protrusions; (2) the etching used in the process offorming the recess/protrusion structure is wet etching, and the shape ofthe bottom surface of the protrusions includes the substrate crystalshape defined by the wet etching; (3) the bottom surface of a protrusionis wider than that of the top surface in the cross sectional view of thesubstrate, or the bottom surface of a recess includes the top surfacethereof in plane view of the substrate, in which the shape of the bottomsurface is approximately polygonal, the top surface is approximatelycircular or approximately polygonal with the sides more than that of thebottom surface; (4) the shape of the mask is approximately circular andthe shape of the bottom surface is approximately a curve of constantwidth or Reuleaux polygon; and (5) in the first main surface of thesubstrate, the protrusions are arranged periodically and the periodicarrangement is triangular, quadrangular, or hexagonal lattice.

The semiconductor light emitting element of the present invention iscapable of preferable light extracting by the optical structure of thesubstrate thereof. Further, in a manufacture of the substrate of theelement having a complicated shape with excellent optical properties,the number of processes is not needed to be increased while exhibitingexcellent mass productivity. Moreover, in a manufacture of the element,suitable semiconductor crystal growth can be realized even with asurface having a recess or protrusion by combining specific shapes oftop surface and bottom surface or side surfaces thereof. Accordingly,the invention can be applied to other semiconductor elements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic plan view illustrating a substrate according toan embodiment of the present invention.

FIG. 1B is a schematic cross sectional view taken along a section lineB-B of FIG. 1A.

FIG. 2( a) is a schematic perspective view and

FIG. 2( b) is a schematic plan view each illustrating arecess/protrusion (a protrusion) of a substrate according to anembodiment of the present invention.

FIG. 3 is a schematic perspective view illustrating a substrateaccording to an embodiment of the present invention.

FIG. 4( a) is a schematic perspective view and

FIG. 4( b) is a schematic plan view each illustrating arecess/protrusion (a protrusion) of a substrate according to anembodiment of the present invention.

FIG. 5( a) is a schematic perspective view illustrating a substrate and

FIG. 5( b) and FIG. 5( c) are schematic plan views each illustrating aconfiguration of recess/protrusion of a substrate according to anembodiment of the present invention.

FIG. 6( a) is a schematic plan view illustrating a light emittingelement and

FIG. 6( b) is a schematic plan view illustrating a substrate of thelight emitting element according to an embodiment of the presentinvention.

FIGS. 7A(a) and 7A(b) are schematic cross sectional views illustrating amethod of manufacturing a substrate according to an embodiment of thepresent invention.

FIGS. 7B(a) through 7B(C) are schematic cross sectional viewsillustrating a method of manufacturing a substrate according to anembodiment of the present invention.

FIGS. 7C(a), 7C(b) and 7C(c) are schematic cross sectional viewsillustrating a method of growing a semiconductor in manufacturing asemiconductor substrate according to an embodiment of the presentinvention.

FIG. 8 is a schematic plan view illustrating a growth method of asemiconductor on a substrate of an element according to an embodiment ofthe present invention.

FIG. 9 is a schematic cross sectional view illustrating a function of asubstrate and a light emitting element according to an embodiment of thepresent invention.

FIG. 10 is a schematic cross sectional view illustrating a lightemitting device using a light emitting element according to anembodiment of the present invention.

FIGS. 11( a) and 11(b) are graphs showing radiation properties in adirection along line A-A (FIG. 11( a)) and along line B-B (FIG. 11(B)),of the light emitting element (FIG. 11( c) according to Example 3 (shownin solid lines) and Comparative Example 1 (shown in dotted lines)according to the present invention.

FIGS. 12( a) and 12(b) are graphs showing radiation properties in adirection along line A-A (FIG. 12( a)) and along line B-B (FIG. 12( b)),of the light emitting element (FIG. 11( c)) according to Example 3(shown in solid lines) and Comparative Example 1 (shown in dotted lines)according to the present invention.

FIG. 13 is a schematic plan view illustrating a recess/protrusion (aprotrusion) of a substrate according to an embodiment of the presentinvention.

FIGS. 14( a) and 14(b) are graphs showing radiation properties in adirection along line A-A (FIG. 11( a)) and along line B-B (FIG. 6( a)),of the light emitting element (FIG. 6( a) according to Example 4 (shownin solid lines) and Comparative Example 2 (shown in dotted lines)according to the present invention.

FIGS. 15( a) and 15(b) are schematic plan views respectivelyillustrating a substrate according to an embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERABLE EMBODIMENTS

The preferred embodiments of the present invention will be describedbelow with reference to the accompanying drawings. However, the lightemitting elements and light emitting devices discussed below are merelygiven to embody the technological concept of the present invention, andthe present invention is not limited thereto. Unless otherwisespecified, the sizes, materials, shapes, relative layouts, and so forthof the constituent members are for illustrative examples, and do notintend to limit the invention therein. The sizes, positionalrelationships, and so forth of the members shown in the drawings may beexaggerated for clarity. In each constituting component of the presentinvention, multiple components may be constructed using the same memberso that one member can serve as multiple components, or vice versa, afunction of a member may be shared by multiple members.

Embodiment 1 Semiconductor Light Emitting Element and Substrate Thereof

A semiconductor light emitting element of the present invention has, asshown in FIG. 9 and the like, basically, a light emitting elementstructure made of a semiconductor layered structure 20 is provided on asubstrate 10. A structure having optical function such as reflectionand/or refraction of light corresponding to light from the lightemitting element is provided mainly on a semiconductor side of asemiconductor growth substrate 10 (a first main surface). Specifically,as shown in FIG. 9, a recess/protrusion structure 11 is provided on afirst main surface of the substrate. The recess/protrusion forms aninterface having an optical function with a semiconductor havingdifferent refractive index than that of the substrate so as to reflectand/or refract light propagating in lateral direction (shown by anoutline arrow in the figure) at the recesses or protrusions, especiallyat an inclined side surface, as indicated by arrows in the figure. Asemiconductor having a structure of light emitting element is providedon the substrate via an under layer if needed.

Specifically in planar view, as an example according to Example 1 andshown in FIGS. 1 to 3, a protrusion preferably has different shapes atits bottom and top surfaces, in particular, the contours of the surfacesare different each other, such as, an approximately triangular bottomsurface 14 and an approximately circular top surface 13. Especially, asin this example, a shape preferably includes a polygonal bottom surface,a top surface having a polygonal shape with a larger number ofconstituent sides than that of the bottom surface, preferably anapproximately circular shape, and a side surface having a larger numberof surfaces than the number of constituent sides of the bottom surface.In an element having a light emitting structure on its substrate, lighttraverses in various directions in the substrate surface. In thisregard, preferable irregular reflection and/or diffraction of light tendto be obtained by the protrusions located at a deeper portion of thesubstrate (bottom surface 12 of a recess) and their inclined sidesurfaces 17 protruding from the bottom surface. In addition, because thetop surface side shows less directional dependence and greater order ofrotational symmetry to the light in various directions than that of thebottom or side surfaces side, directional deviation of light tend to besuppressed at the top surface side. In the present embodiment, FIG. 1Ais a schematic planar view illustrating shapes and arrangement ofprotrusions 11 provided on the surface of the substrate 10, and FIG. 1Bis a schematic cross sectional view illustrating a part of a crosssection thereof. FIG. 2( a) is a schematic perspective view and FIG. 2(b) is a plan view each illustrating a shape of a protrusion 11 indetail. FIG. 3 is a schematic perspective view illustrating protrusions11 provided on the substrate surface.

In detail, as shown in FIG. 2, the bottom surface 14 has a shape convexoutwardly with respect to the triangle 14 a shown in dotted linesconnecting the three tips of the bottom surface 14 in the figure. Twoside surfaces 17-1, 17-2 and two constituent sides 16-1, 16-2 of thebottom surface are provided to each side of the triangle 14 a. Thestructure described above is preferable because the optical performancedescribed above can be improved by providing a greater number of sidesurfaces and inclined surfaces than the number of constituent sides 14 awhich connect vertexes of the bottom surface of a protrusion; that is, acomplex surface formed of a plurality of side surfaces and inclinedsurfaces. In this example, a surface similar to sapphire R-plane can beobtained with the constituent sides 16-1 and 16-2. Herein, vertexes atthe bottom surface are formed with a smaller angle than that of thevertexes of sides 16-1 and 16-2 of the complex surface.

Other examples of the shape of the protrusion 11 provided on thesubstrate include the shapes shown in FIG. 4. In the example shown inFIG. 4, the top surface 13 of a protrusion is triangular and the bottomsurface 14 of the protrusion is hexagonal formed by connectingrespective vertexes of two triangles 14 a and 14 b which are formed byconnecting respective vertexes. FIG. 4( a) is a schematic perspectiveview and FIG. 4( b) is a schematic plan view of a protrusion of Example2. The triangular shapes 14 a and 14 b at the bottom of the protrusionmay be approximately the same size as shown in FIG. 4( a), one oftriangular shape 14 a may be larger than the other triangular shape asshown in FIG. 4( b), which is the case in Example 2. In this example,the larger triangular shape 14 a at the bottom surface has approximatelythe same vertex direction, which is the direction from the median pointto the vertex, as that of the triangular shape of the top surface 13 ofthe protrusion. The other triangular shape 14 b at the bottom surfacehas opposite vertex direction that is a direction rotated at 180° withrespect to the triangular shape of the top surface 13 of the protrusion.In this example, the number of the side surfaces is larger than thenumber of constituent sides of the hexagonal shape of the bottom surface14 of the protrusion. With a complex surface as described above, opticaldirectivity tends to be improved.

As will be described in Example 2, relative to the crystal shape of thesubstrate, that is triangular in the present Example, the mask is formedin a polygonal shape having a larger number of constituent sides or anapproximately circular shape. The protrusions are formed with a shape inwhich the shape of the top surface is similar to the shape of the maskand is different from the crystal shape of the substrate, and the shapeof the bottom surface is similar to the crystal shape of the substrateand different from the shape of the mask. That is, corresponding to twoprincipal shapes of the mask and crystal shape of the substrate, theshape of the bottom surface which is located distant from the maskdepends more on the crystal shape of the substrate and the shape of thetop surface which is located in the vicinity of the mask depends more onthe shape of the mask. That is, the degree of dependence on the crystalshape of the substrate has a gradient that is higher in a portion closerto the bottom surface than a portion closer to the top surface on whichthe mask is provided. By utilizing the dependency, the present inventionprovides a configuration that improves properties such as radiationproperties and crystallinity. As the wet etching progresses, the shapeof the bottom surface becomes triangular similar to the shape 14 a ofthe substrate crystal. Therefore, in the examples shown in FIGS. 1 and13, the etching is stopped before forming such a shape to form thebottom surface with a shape that is wider in cross-section and area thanthat of the crystal shape 14 a. At the same time, due to the circularshape of the mask, a convex planar portion is formed along each side ofthe crystal shape of the substrate 14 a. That is, each side of thecrystal shape 14 a of the substrate defined by the wet etching projectsoutwardly to form a convex portion. In a similar manner, the convexportions are formed in the top surface in an example shown in FIG. 13,in which the degree of projection and curvature of the convex portionsare larger than that of the bottom surface sides.

For example, in Examples 1 and 2 to be hereinafter described, the topsurface of the protrusion portion has approximately the same shape asthat of the mask, in particular, a similar shape to the mask, becausethe corrosion proceeds inwardly from the circumference of the mask.Therefore, as the etching proceeds, the circumference of the protrusionportion approaches to the approximate triangular shape 14 a of thesubstrate crystal. Thus, the shape of the bottom surface side becomesvery similar (Example 1, FIG. 1) to, and on the other hand, it becomesdissimilar (Example 2, FIG. 4) to that of the crystal shape. The topsurface 13 side of the protrusion may be formed to be in the course ofchanging from the mask shape to the substrate shape. That is, as shownin Example 4 and FIG. 13, the shape can be of an intermediate shapebetween the mask shape and the substrate shape (triangle 13 a in thefigure). Further, as shown in FIG. 4, the protrusion can be formed suchthat the side surfaces include multiple surfaces to form athree-dimensional configuration that is an intermediate shape betweenthe shapes of the top surface and bottom surface, incorporating theconfigurations of the top surface and bottom surface. The side surfacesmay be formed in a similar manner as that of the top surface and thebottom surface.

Moreover, as in the examples to be described hereinafter, the bottomsurface is formed in a shape similar to the shape of the mask (circularor triangular shape) than a triangular shape 14 a which is the shape ofthe crystal, but the shape thereof is not limited thereto and theetching may be further proceeded to form approximately the same shape asthe triangle 14 a. However, an intermediate shape is preferable ratherthan the shape of the substrate crystal because an in-plane orientationdependence of the crystal and emission can be suppressed with theintermediated shape so that the crystal and radiation properties can beimproved. Further, a shape which is approximately a curve of constantwidth or Reuleaux polygon to be described hereinafter is morepreferable.

As shown in Examples 1 and 4, when the shape of the mask isapproximately a curve of constant width such as approximately a circleand the bottom surface side is an intermediate shape between the shapesof the mask and substrate crystal, similarly, a shape which isapproximately a curve of constant width or a similar shape thereto canbe formed. In Examples 1 and 4, the shape of the substrate crystal isapproximately triangular 14 a, so that the shape of the bottom surfaceis approximately a Reuleaux triangle or a similar shape thereof. Thus,when the shape of the substrate crystal is a regular polygon and theshape of the mask is approximately a curve of constant width, inparticular, when the shape of the mask is approximately circular and theshape of the substrate crystal is a regular polygon, the bottom surfaceside can be formed in a shape which is approximately a curve of constantwidth or Rauleaux triangle, or a similar shape thereto. Also, as inExample 4 to be described hereinafter, when the top surface side has anintermediate shape between the shapes of the mask and substrate crystalas in the bottom surface side, the shapes of the top surface and bottomsurface may be approximately a curve of constant width or Reuleauxpolygon (which is an odd-numbered polygon). Examples of the shapessimilar to that described above include such as approximately a Reuleauxpolygon with rounded corners as the top surface 13 of the protrusion inFIG. 13, and shapes in which a part of the curved sides and cornersfragmented to form a polygonal line.

As described above, whether the shape of the top surface side or thebottom surface side is an intermediate shape between the shapes of themask and the substrate crystal, or whether the top surface and thebottom surface of the protrusion portion have different constituentsides, can be determined by the degree of diversion from their nominalcontour that is either the shape of the mask or the shape of thesubstrate crystal. For example, from the ratio between the circumferencelengths (circumference length of the top surface or bottomsurface)/(circumference length of the nominal contour of the top surfaceor the bottom surface) respectively, or the ratio between the areas(area of the top surface or bottom surface)/(area of the nominal contourof the top surface or the bottom surface) respectively. If such a ratiois larger than 1, the number of constituent sides of a top surface sideis larger than that of a bottom surface side, when each intermediateshape has multiple sides. In this case, the nominal contour 13 a of thetop surface preferably has an approximately the same contour as thenominal contour 14 a of the bottom surface, as shown in FIG. 13.

Here, various shapes of the substrate crystal can be formed by selectingthe substrate material, planar orientation thereof, and etchant. In thecase where a dry etching is used, the shape at the substrate side can beformed in a similar manner as in the substrate crystal shape, byadjusting the mask shapes for the upper portion and for the lowerportion as shown in FIG. 7B.

Moreover, protrusions 11 on the substrate are preferably arranged sothat a plurality of protrusions are provided spaced apart from eachother, as shown in FIGS. 1 to 3 and the like. Herein, the protrusionsmay be arranged irregularly. However, an arrangement with high densityis preferable to obtain a suitable light emitting element, and a regulararrangement is preferable to obtain suitable directivity. Periodicarrangement of the protrusions 11 may be a hexagonal lattice (arrangedat each tip of parallelogram 11A or two triangles 11B) as shown in FIGS.1 to 3. The arrangement may also be in triangular lattice, quadrangularlattice and the like, or in a circular pattern and the like. Each of theprotrusion is arranged at each lattice point of a periodic arrangement.Moreover, the periodic or orderly arrangement is preferably formed onthe entire surface of the substrate. However, multiple regions (eachhaving a regular arrangement) may be provided in which a regulararrangement is provided in some regions and a recess-protrusionstructure is not provided in other regions, or a different arrangementthereof in which an irregular arrangement and a regular arrangement areprovided. For example, a long-period regular arrangement, in which anarrangement having a region including regular and irregular structuresand a region of a planar surface of the substrate, may be employed. Theperiodic arrangement may have basic units 11A, in each of which theprotrusions are arranged as described above, aligned in its axialdirections 11 a, 11 b. In the illustrated example, a quadrangular shape(hexagonal lattice) is periodic arrangement of the basic units 11A. Whenthe planar shape of the protrusion is dissymmetric, the directivity oflight can be controlled by also adjusting the direction of the shape.For example, as shown in FIG. 6, the directivity of light can becontrolled by setting a desired relationship between the structures ofthe light emitting element and electrodes and their configuration, andthe direction of an approximately triangular bottom surface of theprotrusion portion. The direction may be either aligned in one directionas in the arrangement of the protrusions described above, or arrangedirregularly or regularly. Desired crystallinity and optical propertiescan be obtained by adjusting the direction. Arranging the protrusions inone direction as shown in FIG. 6 is preferable because a suitablecrystallinity and optical properties can be obtained thereby.

Specific examples of the configuration of the protrusions of thesubstrate include structures shown in FIG. 15 and Examples 5, 6 to behereinafter described, as well as the structure shown in FIG. 1. Thedifference in structure between the embodiment shown in FIG. 1 and FIG.15 is that the direction of the protrusions with respect to the axialdirections 11 a, 11 b. Specifically, the facing directions of theconstituent sides and vertex of the bottom surface of the protrusionswith respect to the aligning directions of the protrusions aredifferent. As an example shown in FIG. 1, each protrusion includesconstituent sides 16C, 16A that are approximately in parallel with thetwo aligning directions 11 a, 11 b respectively, and each of the vertexdirections thereof incline to the corresponding aligning direction. Inthe examples shown in FIG. 15, each protrusion includes constituentsides 16A to 16C, that incline to the two aligning directions 11 a, 11 brespectively, and each of the vertex directions thereof is approximatelyin parallel with the corresponding aligning direction. As the examplesshown in FIG. 15, if the bottom surface is approximately triangular, thealigning directions are preferably approximately in parallel withrespective vertex directions.

An alignment structure of the protrusions having a region with highdensity in terms of reflecting light can be formed with the constituentsides inclining toward the aligning direction as an embodiment shown inFIG. 15. Specifically, the protrusions are arranged along the aligningdirection, and regions between adjacent rows of the protrusions have alow density of the protrusions, so that regions with a low density interms of reflecting light can be formed. Especially, as in the exampleshown in FIG. 1, if the constituent sides 16A and 16C that areapproximately in parallel with respective alignment directions,reflectivity of light decreases in the regions between the rows of theprotrusions, so that regions with further lower density may be formed.Here, such regions between the rows of the protrusions or regions havinga low density in terms with reflecting light are provided in an aligningdirection. Due to the rotational symmetry, a third direction is providedin the examples shown in FIGS. 1, 15, that is 120° rotated from thedirection 11 a, and at an angle with or inclining toward the twoaligning directions 11 a, 11 b of the triangular shapes in the figures.Meanwhile, as in the example shown in FIG. 15, if the constituent sides16A to 16C are provided inclined toward the aligning direction, theinclined sides reflect light that is travelling in the direction of therow. Further, the effect can be increased by narrowing the distanceamong the rows of the protrusions. Specifically, the distance among therows are preferably made narrower, such as from that shown in FIG. 15(a) to that shown in FIG. 15( b). For example, as shown in FIG. 15( b),when adjacent rows B,C of the protrusions are to be provided withrespect to the aligning direction 11 a, the width of the intervalbetween the rows is set narrower than that of the rows B,C. That is, thewidth of a region between the rows of protrusions is preferably madenarrower than the width of a row of protrusions in one aligningdirection so that a part of the adjacent rows of the protrusions overlapeach other. Moreover, it is preferable to apply such arrangement in allaligning directions.

Here, it is preferable to provide a constituent side which is inclinedwith respect to at least one of the aligning direction. More preferably,all of the constituent sides are inclined. Moreover, it is preferablethat at least one constituent side, more preferably all of theconstituent sides are inclined with respect to two aligning directions.Particularly, among the constituent sides, the inclined constituentsides are preferably provided adjacent to the regions between the rowsof the protrusions. In the present specification, the term “incliningdirection” means a direction intersecting with the aligning directionand that includes a perpendicular direction.

In the regions 12A to 12C each of which is a region of recess 12surrounded by protrusions, approximately entire portion of a constituentside of each of the surrounding protrusions is adjacent to the region12A in FIG. 1. On the one hand, a part of each of the constituent sidesof the surrounding protrusions is adjacent to the regions 12B, 12C inFIG. 15 respectively. For example, as the region 12C shown in FIG. 15(b), the region is surrounded by each of the half of the constituent sideof the protrusions. Thus, the density of the protrusions can bepreferably increased by forming the recess regions 12B, 12C smaller,surrounded by a part of the constituent sides of the protrusions. It ispreferable that the area of the enclosed region of a recess 12 can beformed smaller than the area of the bottom surface of a protrusion, sothat a high density of the protrusions and similar reflection of lightas in the region 12A can be obtained.

In a relationship between a light emitting element and arecess/protrusion structure, optical output and light extractionefficiency of a light emitting element depend mainly on the height ofthe protrusion (depth of the recess) and the interval of the protrusions(density of the protrusions). The height of the protrusions (depth ofthe recesses) may be in a range from 0.2 μm to 2 μm, preferably from 0.5μm to 1.5 μm. The interval of the protrusions or the width of therecesses may be in a range from 0.5 μm to 1.5 μm, preferably 3 μm orless. Thus, it is preferable that the recesses or protrusions arearranged at high density. Similarly, the width of the protrusions may bein a range from 0.2 μm to 5 μm, preferably 3 μm or less, so as todispose the protrusion in high density. Not limited to those describedabove, each of the size described above may be set to λ/4 or λ/(4n) orlarger, with respect to the emission wavelength λ of the light emittingelement so as to provide the protrusions with the highest possibledensity. Herein, n represents the refractive index of a medium in whichlight propagates, that is the refractive index of the substrate 10 orthe semiconductor 20 that forms an interface with the substrate.

The shape of the side surface may be, as shown in FIG. 1B and the like,a slope with an acute angle between the bottom surface 14 and the sidesurface 17 or alternatively, a slope with an obtuse angle thereof.However, it is preferable that when the angle is acute, the exposedsurface of the inclined side surface 17 faces toward the semiconductorlayer and suitable propagation of light as illustrated in FIG. 10, thatis a change from lateral direction to longitudinal direction, can beobtained. Specifically, as shown in FIG. 1B, when the bottom surface 14of the protrusion is wider than that of the top surface 13, and further,when the area of the bottom surface is larger than that of the topsurface, and moreover, when the top surface is provided within thebottom surface in planar view, optical function at the interface betweenthe semiconductor and the side surface 17 of the protrusion portion ofthe substrate can be improved, and therefore, preferable.

The relationship between the shape of the protrusion 11, especially, theshape of the side surface 17 or the top surface 13 of the protrusion orthe bottom surface 14 and the semiconductor light emitting element ispreferably, as described above and as shown in FIG. 9, such that theside surface is inclined from the normal line of the top surface of thesubstrate 13 and/or the bottom surface 14 or the stacked structure ofthe semiconductor 20. As shown in FIGS. 1 to 3, in the surface of thesubstrate, the constituent sides 16 of the bottom surface 14 of theprotrusions 11, which are facing each other with a recess portion 12 inbetween, are preferably such that the direction thereof is not being inparallel, but being in a different direction so as to cross each other,preferably in a direction also inclined from the perpendiculardirection, because the directional dependency within the plane can bereduced and directional characteristics of emission can be improvedcompare to the case where the sides are in parallel. Further preferably,as shown in FIG. 1A, the constituent sides 16 of the bottom surface ofthe protrusions 11, that are the three protrusions 11 in the exampleshown in FIG. 1A, forming a part of the periphery of a region 12A of arecess 12 are aligned each other in a direction inclined from theperpendicular or parallel directions. Because a further preferabledirectivity of light tends to be obtained compared to the cases wherethe sides are arranged in perpendicular or parallel direction.

Herein, although the sides 16 of the bottom surface of the protrusionare illustrated, planar shapes of the top surface and the side surfacesof the protrusion also show a similar tendency. With an approximatelycircular top surface of the protrusions as shown in FIGS. 1 to 3, theprotrusions surrounding a recess 12 are in a configuration in which theprotrusions are inclined each other in the parallel or perpendiculardirection. As described above, when the top or bottom surface of theprotrusion does not include a constitutive side, the above can beapplied to the end portions 15 or 16 of the top or bottom surfaces, orto a part thereof. However, as described above, a side is preferablyincluded at least in the bottom surface which has a wider cross section.Because there is a tendency between each portion and the opticalproperties thereof. That is, the effect on optical properties is largerwith the shape of the bottom surface 14 than with the shapes of the sidesurfaces 17 and the top surface 13, and less with the shape of the topsurface 13 than with the shapes of the bottom surface 14 or the sidesurfaces 17. Especially, the effect thereof becomes more significantwhen the cross section of bottom surface is larger than that of the topsurface, and further, when the bottom surface has a large area. That is,the effect described above becomes significant when the outercircumference of the constituent sides and the end portion 16 of thebottom surface is larger than that of the top surface.

Embodiment 2 Method of Manufacturing Substrate and Element Using theSubstrate

A method of manufacturing the above-described substrate and element willbe illustrated in Embodiment 2 below and a substrate for light emittingelement and an element will be illustrated thereafter.

In a method of manufacturing above-described protrusions shown in FIGS.1 to 4, as shown in FIG. 7, a mask 19 is formed on the substrate and theprotrusions with a top surface, bottom surface and side surface, eachhaving a desired shape described above, are formed by etching thesubstrate. Examples of etching include wet etching and dry etching thatwill be described hereinafter. As a dry etching, vapor phase etching,plasma etching, or reactive ion etching may be employed. Examples of theetching gas include, a chlorine-based gas and a fluorine-based gas suchas Cl₂, SiCl₄, BCl₃, HBR, SF₆, CHF₃, C₄F₈, CF₄ and the like, and aninactive gas such as Ar.

In the cases where dry etching is employed, as shown in FIG. 7B, theshape of the protrusion described above is formed by forming a maskhaving a three-dimensional shape or by performing the etching at leasttwo times using masks with different shapes. Therefore, compared to thatof wet etching, productivity and degree of accuracy of the shape of theprotrusions may not be sufficient. Specifically, at least two masks of alower mask 19 a and an upper mask 19 b provided thereon are formed withpredetermined shapes, in particular, with different shapes, so that thetop surface of the protrusion and/or the lower mask 19 a are formed withpredetermined shapes (FIG. 7B(a)) by using the upper mask 19 b. Then,when the substrate is etched through the two masks 19 a and 19 b, eachof the masks is also etched (FIG. 7B(b)) as well as the substrate. Byperforming further etching, the upper mask 19 a is removed andprotrusions having top surface, bottom surface, and side surfaces in thepredetermined shapes described above are formed (FIG. 7B(c)). Thus inthis embodiment, the second mask 19 b at the upper side mainly definesthe shapes of the first mask 19 a at the lower side and/or the top andupper portion of the side surfaces of the protrusions. The first mask 19a at the lower side mainly defines the shapes of the bottom surface ofthe protrusions and moreover, the shapes of the side surfaces of theprotrusions.

To define a mask material, two resist materials, such as a resist filmand an inorganic compound such as an oxide or nitride of silicon,aluminum and the like, can be used. When two materials having differentexposure sensitivities are used, two layers are coated or formed andthen exposed respectively to form predetermined shapes. Herein, theupper layer side can be formed with its predetermined shape afterforming the lower layer side with its predetermined shape. Reversely,the upper layer side and lower layer side can be formed in sequence andthe upper layer side and lower layer side are processed in sequence toobtain the predetermined shapes. Alternatively, by using the second mask19 b of the upper layer side, the first mask 19 a of the lower layerside can be formed with a desired three-dimensional shape.

Herein, FIGS. 7A(a), 7A(b) and FIGS. 7B(a) to 7B(c) are schematiccross-sectional views respectively showing an example of a method ofmanufacturing a substrate of the invention, and FIGS. 7C(a) to 7C(c) areschematic cross-sectional views showing an example of a method ofmanufacturing an element by growing a semiconductor on the substrate.FIGS. 8( a) and 8(b) are schematic plan views showing a substrate havinga recess/protrusion structure and illustrating a growth of asemiconductor on the surface thereof. In the following, a manufacturingmethod thereof according to the invention will be described withreference to the figures.

Referring to FIGS. 7A(a) to 7C(c), a basic embodiment of a process offorming the protrusions 11 of a substrate by using the above-describedetching will be described below. A protective film 19, which is to be anetching mask, is disposed and defined into a predetermined shape on asubstrate 10, as shown in FIG. 7A(a). A substrate capable of growing asemiconductor thereon, such as a sapphire substrate in an example, isused for the substrate 10. The protective film 19 may be formed with apattern corresponding to approximately the same shape as the shape ofthe top surface 13 of the protrusions in a planar configuration such asa circular shape shown in FIGS. 1 and 3, to form a mask 19.

Next, as respectively shown in FIGS. 7A(b) and 7B(b), the protectivefilm 19 and the exposed surface of a substrate 10 are etched. Either dryetching or wet etching described above can be used for the etching, andwet etching is preferably used. This is because when wet etching isused, the surface of the protrusions can be made smoother whichcontributes to improve crystallinity and with good mass productivity.Moreover, the shape of the bottom surface of the protrusions and furtherthe shape of the top surface thereof can be formed easily with a shapethat is an intermediate shape between the crystal shape of the substrateand the shape of the mask as described above. As the etching solution inwet etching, for example, for a sapphire substrate shown in the example,phosphoric acid or pyrophosphoric acid, a mixed acid of phosphoric orpyrophosphoric acid with additional sulfuric acid, or solution ofpotassium hydroxide can be used. As the etching solution, variousetchants can be used as the etching solution according to each materialof the substrate, and typically, a high temperature etching solutionsuch as hot phosphoric acid is used as shown in the embodiment. Otherthan an oxide of silicon such as SiO₂ shown in the embodiment, the maskmaterial is suitably selected according to the substrate material andthe etching solution. The examples of such material include an oxide ofat least one element selected from the group consisting of V, Zr, Nb,Hf, Ti, Ta, Al, and a nitride of at least one element selected from thegroup consisting of Si, B, and Al.

Next, specific examples of forming the protrusions by way of wet etchingwill be described below.

As shown in FIGS. 7A(a) and 7A(b), the mask 19 is formed with apredetermined shape and a periodic or regular structure, and then wetetching is performed. Accordingly, as shown in FIG. 7A(b), as theetching progress, the protrusions are formed under the mask, with ashape according to the present invention. Thus, the protrusions eachhaving a top surface smaller in width and area than that of the mask canbe obtained. Typically, a surface and a shape that depend on the planarorientation of the substrate crystal are formed by wet etching. However,by controlling the planar shape of the mask and the amount of etching,the protrusions, especially the bottom surface and the side surfacesthereof, can be formed with above-described shapes of the presentinvention. The shape of the top surface of the protrusions mainlydepends on the mask shape as described above, so that the top surfacecan be formed with a similar shape as the mask shape, specifically,approximately homothetic to the mask shape.

Generally, etching of a C-plane sapphire substrate results in atriangular pyramid shape having a triangular bottom surface. Therefore,as shown in FIGS. 1 to 3, in a case where the protrusions are formedwith a circular top surfaces and an approximately triangular bottomsurfaces (in which each side of a bottom surface includes two sides16-1, 16-2 and two side surfaces 17-1, 17-2), by using a circular mask,a circular top surfaces which are similar shape as the mask are formed,and an approximately triangular bottom surfaces (each having sixconstituent sides in total) which are analogous form as a triangularshape of the crystal, are formed. In an example shown in FIG. 4, etchingis performed by using a mask having approximately regular triangularshape that is rotated 180° in relation to the approximately triangularshape 14 b of the etching surface. Thus, the protrusions can be made ina composite shape made up of the top surface shape which depends on themask shape and the bottom surface shape which depends on the etchingproperties of the substrate, such as a composite shape made up of thecrystal shape of the substrate and the mask shape. That is, a compositeshape made up with the constituent sides 14 of the bottom surface, theside surfaces 17-2 depending on the top surface shape, and the sidesurfaces 17-1 and 17-3 (providing the constituent sides 16-1 a, 16-2 a)depending on the etching properties can be obtained. As described above,the shape of the protrusion portions of the substrate according to thepresent invention can be made with the shapes and the number of theconstituent sides different in the top surface and the bottom surface,by utilizing the etching properties.

In addition, when the amount of wet etching is further increased in anexample shown in FIG. 7A, the cross-sectional width and the area of thetop surface can further be reduced. Therefore, a shape having little orno top surface such as a pyramid, a hemisphere or semicircular shape,and an acuminate or curved shape can be made. As will be hereinafterdescribed, a suitable crystal growth of a semiconductor can be obtainedwhen the growth of the semiconductor occurs from the top surface,compared with the case in which a growth from the top surface did notoccur. That is, with the growth from the top surface, formation of voidsdue to uneven surface, deterioration of crystallinity, and decrease inthe effect of lowering the crystal transition can be prevented.

A method of growing a semiconductor on a substrate surface by using asubstrate provided with the protrusions described above, and forming asemiconductor substrate will be described below. Although the shape ofthe protrusions of the substrate is similar to that described inEmbodiment 1, the planar orientation thereof becomes important. Because,a crystal growth on a substrate depends on the epitaxial growth of thesemiconductor crystal. Therefore, it is important to adjust the shape,periodic or regular structure, and the orientation appropriate for thecrystal growth.

For example, when the substrate 10 is a C-plane sapphire substrate andthe semiconductor 21 is GaN grown in the c-axial direction, the GaNcrystal typically grows with a planar orientation rotated 30° around thec-axis in relation to the planar orientation of the sapphire substrate.Accordingly, the shape of the protrusions 11, especially the bottomsurface thereof, is preferably formed in a polygon as described below.That is, the planar shape of the protrusions 11 is made to be a polygonhaving the sides approximately in parallel with the A-planes of GaN (1 1−2 0), (1 −2 1 0), and (−2 1 1 0), and having vertexes in the stablegrowth surfaces of GaN (1 −1 0 0), (0 1 −1 0), and (−1 0 1 0). Thepolygon is based on a polygon formed with the sides in the stable growthplanes (1 −1 0 0), (0 1 −1 0), and (−1 0 1 0). In other words, thepolygon does not have any sides in parallel with the M-plane and formedwith the sides that are in the directions intersecting to the M-plane.When the protrusions 11 are formed in such shapes, a GaN that is flatand having excellent crystallinity can be grown. In FIGS. 1 to 3, thedirection of A-axis of the substrate (a direction within the substratesurface that is perpendicular to A-plane) is indicated by arrows A.Specifically, when the planar shape of the protrusions is anapproximately regular triangle, the sides of the regular triangle of theprotrusions 11 are preferably formed so as to intersect with the M-planethat is a stable growth plane of GaN in a view from above the substrate.

This is thought that, as shown in FIGS. 7C(a) and 7C(b), the growthspeed of GaN is higher at the joining portion between the GaN grown fromthe top surface of the protrusions 11 and the GaN grown from the flatsurface (recesses 12) where a protrusion 11 is not formed. That is, fromthe top surface of protrusions 11, GaN crystal 21 a is grown in ahexagonal shape with the sides along A-axis as shown in FIGS. 8( a) and8(b). Here, the growth speed of GaN increases at the joining portions inthe vicinity of the side surfaces of the protrusions between GaN crystal21 a grown from the top surfaces 13 of the protrusions 11 and GaNcrystal 21 b grown from the flat surfaces 12. Therefore, the growth ofGaN in the vicinity of the side surfaces of the protrusions 11 catch upwith the other portions, so that GaN with flat surface can be obtained.

The protrusions to the substrate for growing semiconductor may be formedin the shapes as typically shown in FIGS. 1 to 3. For example, as shownin FIGS. 7C and 8, in the early stage of crystal growth, the crystalportions 21 a growing on the top surface of the protrusions and thecrystal portions 21 b growing on the surface of the recesses areseparately grown (FIG. 7C(a), FIG. 8( b)). Then, each of the crystalportions 21 a and 21 b further grow and overlap each other at leastpartially at their side surfaces to form crystals 21A and 21B (FIG.7C(b). Thereafter, uneven portion of each of the crystal portions 21Aand 21B are smoothed to form a semiconductor layer 21. As describedabove, it is preferable to grow the crystal so that the recesses arefilled with the crystal to prevent void formation, and that results inimprovement of the optical properties in the above-describedembodiments. In this example, there is little growth at the sidesurfaces 17 of the protrusions. However, crystal growth from the sidesurfaces may be possible by adjusting factors such as the substratematerial, the shape of the protrusion portion, the semiconductormaterial, and planar orientation of each crystal.

As described above, in order to fill the recesses more suitably with thegrowth of the crystal, the angle of inclination θ of the side surfacesof the protrusions is preferably set corresponding to the interval,density, and height of the protrusions, for example to values in thevicinity of 45°, more specifically, in a range between 20° and 70°,further preferably in a range between 30° and 60°. The protrusions andthe interval thereof may be set as that in the above embodiments.Because a suitable growth of crystal become difficult when the intervalor the size of the protrusions is smaller, or the height of theprotrusions is larger. However, with the dimensions described above, asuitable growth can be obtained.

With the growth of a semiconductor layer using the substrate of thepresent invention, the crystallinity of the semiconductor layer can beimproved. Specifically, crystallinity may be decreased when asemiconductor crystal is grown on a foreign substrate due to thedifferences in the properties such as lattice constant and the thermalexpansion coefficient, the crystal structure, and the planarorientation. However, according to the present invention, suchdisadvantages can be suppressed, or further, penetrating dislocationscan be reduced. This is because as described above, each of thesemiconductor crystal portions 21 a and 21 b grows three-dimensionally,in particular, by a facet grow. Propagation of the dislocations and thelike, occurred at the interface with the substrate can be suppressed ingrowing the crystal, by the lateral growth or overlapping of thecrystals at the side surfaces or in the lateral direction.

Herein, as shown in FIGS. 1 to 4, with respect to the constituent sidesof the bottom surfaces 14 of the protrusions, the sides 16-1, 16-2constructing each of the side, and the side surfaces 17-1 to 17-3, theconstituent segments of a side 14-1 and 14-2 either form a larger anglethan that of the corners of the bottom surfaces 14 of the protrusions oran obtuse angle. Preferably. Each of the sides of the shapes 14 a of thebottom surfaces 14 of the protrusions preferably includes the both.Because, when each of the sides is formed with the constituent segmentsconnecting with an obtuse angle or a large angle, the magnitude of theeffect of crystal growth, that is, a dependence on planar orientationwith the semiconductor crystal described above can be decreased. At thesame time, an appropriate crystal growth and filling of the recessestend to be obtained when a side is formed with a plurality ofconstituent segments. When each side of the shapes 14 a of the bottomsurfaces 14 is connected to a plurality of side surfaces 17-1 to 17-3,at least a part of the sides are formed with the constituent segments(FIG. 4), and preferably, only the side surfaces corresponding to theconstituent segments (FIGS. 1 to 3) are included. Because, as similar tothat in the constituent segments described above, a dependence on planarorientation with the semiconductor crystal described above tends to bedecreased, so that a suitable crystal growth can be obtained. Asdescribed above, the growth of a semiconductor crystal tends to dependon the shape of the bottom surface rather than that of the top surface,and specifically the tendency is significant when the bottom surface iswide. Accordingly, it is preferable to form the bottom surfaces asdescribed above. On the other hand, when the top surfaces have a shapesimilar to the shape shown in FIG. 4, dependency on the shape of the topsurface in the crystal growth increases and it tends to reduce thecrystallinity. However, it can be suppressed by forming the complex sidesurfaces 17-1 to 17-3 as described above. More specifically, as shown inFIGS. 1 to 4, the sides of the bottom circumference are formed tooutwardly protrude from the bottom surface shape 14 a, with theconstituent sides 14-1, 14-2 and the side surfaces 17-1 to 17-3connecting to each side. Thus, the protrusions can be made with apolygonal shape having a large number of sides, with a rounded shape ofthe polygon, and further, with an approximately circular shape. Thus, itis preferable because an appropriate crystal growth, specifically of thecrystal 21 b from the recess portion 12 can be obtained.

FIGS. 5( a) to 5(c) illustrate a first main surface 10A of a substrate10 and its inclination or off-angle, and a difference in theconfiguration and periodic structure of the protrusions formedaccordingly. FIG. 5( a) is a schematic perspective view illustrating aninclination of a substrate, FIGS. 5( b), 5(c) are plan viewsrespectively illustrating a configuration of the protrusions due to theinclination of the main surface 10A of the substrate. Specifically,FIGS. 5( b) and 5(c) are views showing two exemplary configurationswhich are dependant on the off-angles and are obtained by applying wetetching on a C-plane sapphire substrate, as shown in Example 1.

The inclination of the substrate main surface 10A may be defined in twodirections as shown in the figure. An inclination relative to the axisof rotation in the direction of the normal line of the orientation flatplane 18 (A in the figure), and an inclination relative to the axis ofrotation in the direction perpendicular to the normal line of the firstmain surface (B in the figure). For instance, in Example 1 to bedescribed later where the first main surface 10A is off-angled withrespect to the C-plane as the main surface and the orientation flatsurface 18 as the A-plane, two configurations (FIGS. 5( a) and 5(b)) maybe provided with respect to the direction of the triangular shapes 14 aon the bottom surface in the shape of the protrusions shown in Example1, corresponding to the inclination in the rotational direction of theA-axis (B in the figure). On the other hand, the degree of inclinationangle is set lower with respect to another axis in the example.Therefore, a difference in the configurations is not apparent.

Thus, in the case where different configurations of the protrusions 11(the top surfaces 13 and the bottom surfaces 14 thereof) may be providedto the substrate corresponding to the off-angle of the main surface, theshape of the protrusions is preferably formed according to the presentinvention as described above. In the case where the off-angle isfluctuate depending on the substrate, or where the off-angle isfluctuate within the substrate surface, problems arose in thesemiconductor layer growth due to the difference in the shapes of theprotrusions, in controlling the growth, and eventually in the massproductivity. However, such disadvantages can be solved according to thepresent invention. Variation in off-angle in the substrate surface willresult in occurrence of regions having different configurations in theshapes, direction, and periodic structure of the protrusions within thesubstrate surface. In the above-described example, two regions havingdifferent configurations are formed. In this example, the degree ofoff-angle in the configuration shown in FIG. 5( b) is greater than 0, inspecific, in a range from 0.05° to 0.25°, and that shown in FIG. 5( c)is smaller than 0, in specific, in a range from −0.05° to −0.25°.

In the above-described example, each angle is set in a range ofrelatively low angles, specifically from +0.5° to −0.5°. It is thoughtthat if each angle is in a higher range, dependency arises correspondingto each angle of inclination and their compound angles.

Other structures and members in each embodiment illustrated above willbe described below.

(Substrate)

In the present invention, a light transmitting substrate is used for alight emitting element employing a nitride semiconductor. Specificexamples include an insulating substrate of sapphire substrate or spinelsubstrate, and an electrically conductive substrate such as SiCsubstrate and GaN substrate. It is preferable to use a lighttransmitting substrate having a large difference in the index ofrefraction with respect to that of the semiconductor material. Morespecifically, for example, a sapphire substrate having a C-plane (0001)as a main surface can be used as the above-described substrate. Thestable growth plane of a GaN-based semiconductor layer is an M-plane {0−1 0 0} of a hexagonal crystal. Here, “−1” in Miller index indicates “1”with a bar on top. In this specification, Miller index will be shown inthe same manner. Here, {1 −1 0 0} represents (−1 1 0 0), (0 1 −1 0), (−10 1 0) and the like. In a c-axis oriented GaN-based semiconductorcrystal, an M-plane is one of the planes parallel to the A-axis withinthe substrate surface. Other planes that include the A-axis of GaNsemiconductor in the substrate surface, namely planes other than theM-plane, such as the facet of {1 −1 0 1} plane may also become thestable growth plane, depending on the growing condition. In the case ofa C-plane sapphire substrate, the M-plane that is the stable growthplane of the GaN-based semiconductor layer is the plane parallel toA-plane {1 1 −2 0} of the sapphire substrate. The A-plane {1 1 −2 0}represents (1 1 −2 0), (1 −2 1 0), (−2 1 1 0) and the like.

A substrate used for a semiconductor element other than a light emittingelement is needed to be not only light transmissive but to allowsuitable growth of semiconductor. For example, by using a foreignsubstrate such as Si substrate for a nitride semiconductor and therecess or protrusion structures according to the present invention, asemiconductor element excellent in crystallinity can be obtained.

(Light Emitting Element)

In the structure of the light emitting element, a semiconductorstructure 20, specifically a layered structure 20 having each of thesemiconductor layers stacked is provided on a substrate as shown inFIGS. 6, 9 and the like. A structure without having a substrate, whichis obtained by removing the substrate and the like, a structure withouthaving a semiconductor layer such as an underlayer 21 other than activeregion of the element, an element region or structure provided with aconductive region in the substrate, may also be employed. In the lightemitting structure, a light emitting region of the semiconductorstructure 20, and further, a first and second electrodes 30, 40 on thesame surface side are provided, as illustrated in an example shown inFIG. 6, in which a first and second conductive-type layers 22, 24 and anactive layer 23 therebetween are provided. With this electrodestructure, a first electrode 30 or an exposed region 22 s of a firstconductive-type layer, and a region of light emitting structure are atleast arranged in the element region within the substrate surface. Thelight emitting structure preferably has such active layer or lightemitting layer between the first and second conductive type layers.Also, a structure having a p-n junction as the light emitting part, alight emitting structure having a p-i-n structure, a MIS structure andthe like may be employed. In addition, a semi-insulating or insulatingportion, an i-type layer, or a reverse conductivity type layer or regionmay be provided to apart of element structure or each conductive typelayer. For example, a current blocking layer or region formed with suchas a semi-insulating or insulating portion, or an i-type layer, areverse tunneling layer formed with a reverse conductive type forcontacting with an electrode, may be provided to the structure.

(Electrode)

In the light emitting element structure in which the first and secondelectrodes are provided on the substrate and the electrode forming sideis the main emitting side, the first layer of the first electrode 30 andthe contact layer 41 of the second electrode are formed as lighttransmissive films. Examples of the light transmissive conductive filmand a p-side electrode of a nitride semiconductor include at least onemetal selected from the group consisting of Ni, Pt, Pd, Rh, Ru, Os, Ir,Co, Ag, an alloy and a layered structure thereof, and further, acompound thereof such as a conductive oxide or nitride. Examples of aconductive metal oxide (oxide semiconductor) used for the first andsecond electrodes include indium oxide doped with tin (Indium Tin Oxide;ITO) having a thickness of between 5 nm to 10 μm, ZnO (zinc oxide),In₂O₃ (indium oxide), and SnO₂ (tin oxide), a compound thereof such asIZO (Indium Zinc Oxide). Such materials are preferably used because oftheir advantage in light transmissive properties, and a suitablematerial is selected according to the wavelength of light. In addition,constituent element of the semiconductor, dopant of the semiconductor,and the like can also be used for a doping material for the conductivematerials described above.

(Light Emitting Structure and Electrode Structure)

The light emitting structure is selected suitably according to the areaand properties of the element. That is, a single light emittingstructure may be provided in a light emitting element region as shown inFIG. 6, or a region such as an exposed region 22 s of the firstconductive type or a first electrode forming region may be interposed ina part of a light emitting structure. The light emitting structure andthe first electrode 30 are not needed to be one-one relation and otherrelations such as two-one relation as in the structure where the lightemitting structure is arranged between the first electrodes 30 may beemployed, as long as the structure includes at least a set of a lightemitting structure part and a first electrode 30 providedcorrespondingly thereto. As described above, when the main surface ofthe electrode forming side of the substrate is the light extractingside, a light transmissive electrode is used. As shown in FIG. 10, whenthe main surface of opposite side of the semiconductor that is the backsurface side of the substrate is light extracting side, a reflectiveelectrode is used. In addition to this, a structure may be employed inwhich each of the opposite main surfaces of the semiconductor isprovided with an electrode.

A nitride gallium-based compound semiconductor material for a lightemitting element or a semiconductor grown on a substrate is preferablyrepresented by a general formula In_(x)Al_(y)Ga_(1−x−y)N (wherein 0≦x≦1,0≦y≦1 and 0≦y+x≦1), and as described later, a binary mixed crystal orternary mixed crystal thereof can be suitably used. Other than a nitridesemiconductor, the above can also be applied to other semiconductormaterials such as GaAs- or GaP-based compound semiconductor and AlGaAs-or InAlGaP-based compound semiconductor.

(Protrusion, Optical Structure Portion)

A structure such as protrusions having optical functions such asreflection, dispersion, diffraction, and emitting aperture may beprovided to a semiconductor staked structure, for example, to an exposedsurface of the first conductive type semiconductor layer between theelectrode 30 and light emitting structure. A similar effect can beobtained by providing a recess/protrusion structure to the semiconductorstructure portion in a similar way as the above-describedrecess/protrusion structure of the substrate (FIG. 10). Such opticalstructure is preferably formed with a light transmissive insulatingmaterial with reduced light absorption and loss such as arecess/protrusion structure provided by a protective film on the exposedsurface 22 s of the first conductive type semiconductor layer. In so faras the functions of reflection and dispersion, a metallic protrusionportion or recess/protrusion portion can be provided thereon. Becausethe region between the electrode and light emitting structure is narrow,providing a semiconductor structure, for example, the recess/protrusion50 portion as shown in FIG. 11( c), divided from the layered structureof the semiconductor, specifically from the light emitting structure, ispreferable than providing an additional structure. With thisarrangement, the optical structure can be formed with high accuracy andhigh density so that the optical function thereof can be improved.Further, it is preferable because a light transmissive material similarto that of the light emitting element is used for the structure.

A known material having appropriate light transmissive properties, suchas an oxide or nitride of silicon and an oxide of aluminum, may bepreferably used for a protective film provided at the sides of thesurface of the semiconductor layer 20 and the electrode surface of thelight emitting element, according to light and wavelength of the lightemitting element. The thickness of the film may be about 0.1 to 3 μm,and preferably about 0.2 to 0.6 μm.

Such recess/protrusion structure 50 may be formed with separatedprotrusions, for example, an approximately circular in planar shape, byproviding a separating groove from the light emitting structure of thesemiconductor structure. On the other hand, a complex structure may beformed in which an opening (recess) is formed in the light emittingstructure. A planar shape of such protrusion or recess is mostpreferably circular which allows an arrangement of high density withgood mass productivity, but shapes such as elliptic, square orrectangular, polygonal, and a complex shape thereof may also beemployed. A configuration such as square or rectangular, parallelogram,triangular, hexagonal or honeycomb lattice is suitably selected toobtain a high density configuration, according to the planar shapedescribed above. When the planar shape of these structural componentssuch as a protrusion, recess, and groove has a width of 0.5 to 5 μm,preferably 1 to 3 μm, preferable production can be performed. Inaddition, the cross-sectional shape thereof may be such as trapezoidalor inverted trapezoidal, rectangular, preferably with a wider bottomsurface and top surface being inclined toward the electrode as in asimilar way as the above-described protrusions of the substrate. Asdescribed above, a protrusion in the present specification is astructural component having an optical properties to provide an opticalfunction at a surface, top surface, or side surface of the semiconductor20 or at an interface with other materials.

(Light Emitting Device)

Next, a light emitting device 200 having the above-described lightemitting element 100 mounted will be described. As shown in FIG. 10, thelight emitting element 100 is mounted on a mounting portion 202 (anopening portion in the light emitting portion 223 in the figure) definedin a region 201 of the substrate of the light emitting device. Examplesof the mounting substrate include a stem 210 for a light emittingelement, a ceramic substrate for surface mounting, and a plasticsubstrate. Specifically, a mounting substrate made of AlN or a substratemade of a metal is preferably used, because a light emitting devicehaving high heat dissipation can be obtained. The mounting surface wherethe semiconductor light emitting element to be mounted is made of ametallic material so that the light extracted from the light emittingdevice is reflected from the mounting surface and a light emittingdevice having suitable directivity of light can be obtained. At an innersurface of the device where the emitted light reaches, such as amounting surface having the light emitting element mounted thereon andthe reflecting surface 203, a metallic material is used for a leadelectrode 210 and the like. The metallic material is preferably capableof effectively reflecting light of a wavelength emitted from the lightemitting device of the present invention. Examples of the metallicmaterial include such as Ag, Al and Rh, and a plated film or the likemay be formed. In an example of the light emitting device, as shown inFIG. 10, the electrode side of the light emitting element 100 is bondedto the mounting substrate 104, which is also a protective elementagainst static electricity, by using an adhesive. The mounting substrate104 side of the layered structure 103 of the light emitting element 100is bonded to the mounting portion 202 of the light emitting device viaan adhesion layer 114. In other cases, the electrode side of the lightemitting element 100 is designated as the emission side, and asemiconductor light emitting element 100, whose second main surface ofthe substrate is provided with a metallization layer, and an eutecticsolder and an adhesion layer, may be mounted on a element mountingportion of a base substrate or a package 220 of a device by way ofthermocompression or the like. The protective element may be mounted onand electrically connected to a mounting portion 222 provided outside ofthe recess 202 of the base material of the device.

Each electrode of the light emitting element is connected to respectivelead electrode 210 of the light emitting device 200 by such as amountingsubstrate 104 and a wire 250, and the light emitting element is enclosedwith a light transmissive sealing member 230. A transparent resin, glassand the like having excellent weather-resistance such as an epoxy resin,a silicone resin, and a fluorocarbon resin may be used as a sealingmember. A material such as a solder such as a eutectic solder, aeutectic material, and an Ag paste may be used as the adhesion memberother than such resin materials. In the example shown in the figure, areflective electrode is used as an electrode of the light emittingelement.

Various emission colors can be obtained by providing a light convertingmember, which is capable of converting at least a part of light from thelight emitting element, in the sealing member 230 or the like, which isprovided on a light path between the light emitting element and thelight outputting portion such as the emission portion 223 in FIG. 10 ofthe light emitting device 200. Examples of the light converting memberinclude a YAG fluorescent material which is suitably used for whitelight emission by combining a blue LED, a nitride fluorescent materialconverting light in near-ultraviolet to visible light to light in yellowto red region, or the like. Especially, for a high luminance, longtimeoperation, a fluorescent material having a garnet structure such as TAGand TAG, for example, (Re_(1−x)Sm_(x))₃(Al_(1−y)Ga_(y))₅O₁₂:Ce (0≦x<1,0≦y≦1, where Re represents at least one element selected from the groupconsisting of Y, Gd, La and Tb) and the like are preferably used.Examples of the nitride-based fluorescent material and theoxynitride-based fluorescent material include Sr—Ca—Si—N:Eu, Ca—Si—N:Eu,Sr—Si—N:Eu, Sr—Ca—Si—O—N:Eu, Ca—Si—O—N:Eu, Sr—Si—O—N:Eu or the like, andrepresented by a general formula L_(X)Si_(Y)N_((2/3X+4/3y)):Eu orL_(X)Si_(Y)O_(Z)N_((2/3X+4/3Y−2/3Z)):Eu (where L is one selected fromamong Sr, Ca, Sr, and Ca). A light emitting device having desiredemission color can be obtained by suitably using the fluorescentmaterial described above or other fluorescent materials. In the exampleshown in the figure, a coating member 105 including a light convertingmember is provided around the element 100.

EXAMPLES

Now examples of the present invention will be described below, but thepresent invention is not limited to these examples and may be applied tovarious other forms on the basis of the technical idea of the presentinvention.

Example 1

A sapphire substrate having a principal plane in C-plane (0 0 0 1) andan orientation flat surface in A-plane (1 −1 2 0) is used. First, a SiO₂film 19 that makes an etching mask is formed on the sapphire substrate10, as shown in FIG. 7A(a). Then, using a photomask, masks 19 eachhaving circular shape of about 2 μm in diameter are arrangedperiodically.

Then, as shown in FIG. 7A(b), the substrate is immersed in an etchingbath containing a mixed acid of phosphoric acid and sulfuric acid asetchant at about 290° C. for about 5 minutes to obtain a depth (heightof protrusions) of about 1.1 μm.

The structure of a protrusion thus obtained on the substrate may have astructure, as shown in FIG. 1A, in which a side of a triangle of thebottom surface 14 is about 3 μm and each of the two sides 16-1, 16-2forming a constituent side 16 thereof shown in FIG. 2 is about 1.5 μm.Such protrusions are arranged periodically with intervals of theprotrusions 11 of about 3 μm, that is the distance between the ends ofthe top surfaces 15, in a basic pattern 11A with a parallelogram, shownin dotted lines, having inner angles of about 60° and 120° (shown insolid lines in FIG. 1A). The constituent sides 16 of the protrusionssurrounding the region 12A in FIG. 1A, that is a constituent side 16 ofeach of the adjacent protrusions 11, are disposed at an angle with eachother inclined from parallel or perpendicular direction, to form a basicunit 11A. The basic unit 11A are aligned periodically at a regularinterval along the axis directions 11 a, 11 b. Here, each of theconstitutive sides of the triangle 14 a of the bottom surface of theprotrusions is formed approximately in parallel with the M-plane of thesubstrate as shown in FIGS. 1 and 3. Further, each constitutive side 14a is formed by corresponding two sides 16-1 and 16-2 as shown in FIG. 2,and the constitutive sides 16-1 and 16-2 are formed approximately inparallel with the R-plane of the substrate.

Then, the substrate is loaded into a MOCVD apparatus, in which a GaNbuffer layer of about 20 nm is grown at a low temperature on a firstmain surface where the above-described protrusion portion is provided,and thereon, a GaN of about 2 μm is grown in the c-axis at a hightemperature (about 1050° C.) to form an underlayer 21. The growth of theunderlayer 21 on the substrate is shown in FIGS. 7C(a) to 7C(c) and8(b). In the early stage of the growth (FIG. 7C(a), FIG. 8( b)), crystalportions 21 a, 21 b are initially grown respectively from the topsurfaces 13 of the protrusions and the bottom surfaces 12 of the recessportions that are the portions between the protrusion portions andseparated each other in the surface of the substrate. As each of thecrystal portions 21 a, 21 b grows, the height of the crystal portion 21b of the recess 12 exceeds that of the protrusion 13 and a part of theside surfaces and facets of the crystal portions 21 a, 21 b jointogether. Thus, as shown in FIG. 7C(b), the crystal portions grown fromthe protrusions and recesses overlap to form the protrusions 21A, 21B,which are grown from the respective crystal portions. Then the bottomportion of the protrusions 21A, 21B join together to form a layer havinga patterned indented surface. With further crystal growth, the patternedindented surface derived from each of the crystal portions flatten outto form an underlayer 21 with a planar surface, as shown in FIG. 7C(c).

In the present example, the top surface of each protrusion is about 1.5μm in diameter, the distance between the top surfaces 13 of theprotrusions (the distance between the ends of the opposite top surfaces15) is about 3 μm, the distance between a vertex of the bottom surface14 of a protrusion and an end 15 of the top surface of the protrusion isabout 1 μm, and the cross-sectional width in the vertex direction (thedirection between a vertex of the bottom surface and the median point ofthe triangle of the bottom surface) is about 3 μm. Angles of inclinationof the side surface 17 to the top surface 13 or bottom surface 14 of theprotrusion are about 80° at a corner of the triangle 14 a of the bottomsurface and about 63° at a corner between the sides 16-1 and 16-2 of thebottom surface shown in FIG. 2.

A semiconductor element is fabricated by forming, for example as shownin FIG. 9, an n-type layer 22 such as an n-type contact layer, an activelayer 23, and a p-type layer 24 on the semiconductor substrate made ofthe underlayer 21 thus obtained. Specifically, a layered structure(emission wavelength of 465 nm, blue LED) may be used, which is formedby stacking, on the underlayer 21, a first conductive type layer 22(n-type layer) including an n-side contact layer of GaN doped with Si of4.5×10¹⁸/cm³ of 5 μm thickness, a multilayer between the contact layerand an active layer including an undoped GaN layer of 0.3 μm thickness,a GaN layer doped with Si of 4.5×10¹⁸/cm³ of 0.03 μm thickness, anundoped GaN layer of 5 nm thickness, and ten layers of alternatelystacked undoped GaN layer of 4 nm and undoped In_(0.1)Ga_(0.9)N layer of2 nm, an active layer 23 having a multiple quantum well structureincluding six layers of alternately stacked a barrier layer of undopedGaN of 25 nm thickness and a well layer of In_(0.3)Ga_(0.7)N of 3 nmthickness, a second conductive type layer (p-type layer) 24 including ap-side multi layer having five layers of alternately stackedAl_(0.15)Ga_(0.85)N layer doped with Mg of 5×10¹⁹/cm³ of 4 nm thicknessand In_(0.03)Ga_(0.97)N layer doped with Mg of 5×10¹⁹/cm³ of 2.5 nmthickness, and an Al_(0.15)Ga_(0.85)N layer doped with Mg of 5×10¹⁹/cm³of 4 nm thickness thereon, and a p-side contact layer of GaN doped withMg of 1×10²⁰/cm³ of 0.12 μm thickness.

On the surface of the p-type layer 24 that is a surface of the lightemitting structure, an ITO of about 170 nm thickness is provided as alight transmissive ohmic electrode 41 of the second electrode 40. Then,a first electrode 30 (n-electrode) is provided on the exposed surface ofthe first conductive type layer (n-side contact layer in the n-typelayer) 22 s, and a pad electrode 42A and wiring electrodes 42B made of asequentially stacked film of Rh (about 100 nm)/Pt (about 200 nm)/Au(about 500 nm) extending from the pad electrode are provided on a partof the light transmissive electrode 41. Each of the electrodes is formedinto a predetermined shape by way of photolithography, and the firstelectrode 30 and the pad electrode 42A of the second electrode 40 areused as external terminals. Then, the LED chips are obtained by dividingthe wafer into light emitting elements of approximately 350 μm square.Suitable scattering and diffraction of light, as shown in FIG. 9, can beobtained by providing the protrusions 11 on the semiconductor layer 20side of the substrate as shown in FIG. 6( b), so that light output powercan be improved. The protrusions 11 in FIG. 6( b) are shown larger thanthe actual size employed in Examples.

The size of each structure shown in the above examples is as follows.The thickness of the substrate 10 is about 50 to 200 μm (about 90 μm inthe above example). In the layered structure 20, the thickness of theunderlayer 21 is about 1 to 3 μm, the thickness of the n-typesemiconductor layer 22 is about 2 to 5 μm, the thickness of the activelayer or light emitting layer 23 is 10 to 100 nm, the thickness of thep-type semiconductor layer is about 100 to 300 nm. The height from theexposed surface of the n-type layer 22 s to the light emitting structureis about 1 to 3 μm (about 1.5 μm in the above example). The thickness ofeach of the first layer (first electrode) and the second electrode(lower layer) is about 0.01 to 0.5 μm. The thickness of the second layerand pad electrode is about 0.3 to 1.5 μm. The width or diameter of theexternal connection portion and the pad electrode is about 50 to 150 μm.The width of the exposed outer circumference of the element 22 s isabout 5 μm to 30 μm.

Example 2

In Example 2, the substrate is formed as in a similar manner as inExample 1, except that the protrusions 11 are formed with a triangularshape at the top surface of the protrusion 13 and the mask 19 foretching, as shown in FIG. 4. As shown in FIG. 4, a mask 19 and the topsurface 13 are configured in a shape rotated by 180° around the medianpoint of the triangle 14 a of the bottom surface. Thus, the protrusion11 having three side surfaces 17-1 to 17-3 corresponding to each side ofthe top surface 13 and the triangle 14 a of the bottom surface. Eachsize of each part of the protrusion 11 is similar to that in Example 1,except that the top surface of the protrusion is approximately regulartriangle with the length of a side of about 1 μm.

Approximately the same crystallinity as in Example 1 can be obtained bygrowing an underlayer 21 in the same manner as in Example 1, on thesubstrate having the protrusions 11.

In Examples 1 and 2, the electrode forming side of the semiconductorlayer side is arranged as the main light extraction surface by using alight transmissive electrode as the electrode and improvement in thelight extraction efficiency due to the recess/protrusion of thesubstrate is obtained. As in the light emitting device described above(FIG. 10), preferable light extracting efficiency can also be obtaineddue to the recess/protrusion of the substrate in the light emittingelement having a reflecting electrode and the substrate side being thelight extraction surface.

Comparative Example 1

In Comparative Example 1, the recesses/protrusions of the substrate areformed by etching using RIE through a mask having approximately the sameshape, size, interval, and configuration as in Example 1. In therecess/protrusion structure of the substrate thus obtained, theprotrusions have a circular truncated cone shape with approximately 0.9μm in height and intervals (between the bottom surfaces) ofapproximately 1 μm. The top and bottom surfaces have approximatelycircular shapes at the top and bottom surfaces with the respectivediameter (cross-sectional width) of approximately 0.6 μm andapproximately 2 μm.

On the substrate having the recess/protrusion structure, an underlayerand a semiconductor element structure are stacked, and each electrode isprovided as in the similar manner in Example 1 to obtain a lightemitting element according to Comparative Example 1.

Here, the light emitting element is formed with a structure and shapedifferent from that in Example, to a 420×240 μm rectangular element asshown in FIG. 11( c).

Example 3

In Example 3, the recess/protrusion structure of the substrate,semiconductor layered structure, electrodes and the like are formed asin a similar manner in Example 1, and a rectangular light emittingelement described above is formed.

Radiation properties thus obtained in Comparative Example 1 and Example3 are shown in FIGS. 11( a) and 11(b), respectively. FIG. 11( a)respectively show the directivity in the A-A line direction and FIG. 11(b) shows the directivity in the B-B line direction, in the plan view ofthe element 11(c). Herein, the directivity according to Example 3 isshown in full line and that to Comparative Example is shown in dottedline.

As shown in FIGS. 11( a) and 11(b), Example 3 shows higher directivitythan that in Comparative Example 1 in the direction of the optical axisperpendicular (90°) to the element surface. Moreover, ascent of thecurve at around 30 to 45° observed in Comparative Example 1 is absent inExample 3. Accordingly, compare to Comparative Example 1, Example 3shows that the intensity along the axis is increased and the fluctuationin the overall directivity decreased, so that the overall directivitybecomes uniform. Thus, a great improvement is obtained. In addition,when a metallic reflection coating (an Al reflecting coating in theexample) is provided on the back surface of the substrate of theelement, a similar tendency in the radiation properties as shown in FIG.12 can be observed in Example 3 (solid line in the figure) and inComparative Example 1 (dotted line in the figure).

In addition, when the underlayer is grown to a thickness of 3 μm and thecrystallinity thereof is evaluated by the rocking curve half-width,approximately 20 to 30% decrease can be observed in (1 0 2) and (0 0 2)planes in Example 3 (Example 1) compared to that in ComparativeExample 1. Accordingly, it is apparent that a great improvement in thecrystallinity is achieved.

Example 4

The recess/protrusion structure is formed on the substrate in a samemanner as in Example 1, except that the conditions of etching andmasking are varied to obtain the protrusions having a planar shape asshown in FIG. 13. The top surface 13 of the protrusions is approximatelycircular due to the shape of the approximately circular mask in Example1 and a intermediate shape between the shapes of the mask and the bottomsurface of the protrusion in Example 4. This is considered that thedependency of the top surface 13 of the protrusions to the shape of themask is decreased by varying the conditions such as the material andadhesiveness of the mask, etching speed, concentration of the solution,so that the top surface has a transitional shape between the shapes ofthe mask and the bottom surface of the protrusion (constitutive sides of16-1, 16-2 of the side surfaces 17-1, 17-2, respectively) which is theetching shape of the substrate crystal.

In such case, the shape becomes closer to a circle, that is the maskshape, compared to the shape of the bottom surface of the protrusion,and a longer curved portion 15-b corresponding to the constitutive sides(16-1, 16-2) of the bottom surface of the protrusion and a shortercurved portion 15-a corresponding to the corners of the bottom surfaceof the protrusion occur at the end portion of the top surface 15. Thecurvature radius of the curved portion 15-b is smaller than that ofcorresponding bottom surface of the protrusion. On the one hand, thecurved portion 15-a has a further rounded shape than that of thecorresponding corner (vertex) of the bottom surface of the protrusion.

Therefore, dependence on the mask shape is lower at the bottom surfaceside and higher at the top surface side. On the other hand, dependenceon the substrate crystal is higher at the bottom surface side and lowerat the top surface side.

A light emitting element of Example 4 shown in FIG. 6( a) is fabricatedin the same manner as in Example 1 and radiation properties are comparedto that of Example 1. Each directional characteristics in A-A directionand B-B direction shown in FIG. 6( a) shows, as in FIGS. 14( a) and14(b), a slight increase in the intensity on the axis (90°) in Example 4compared to that in Example 1. This is considered that the area of thetop surface decreases and in comparison the proportion of the sidesurface to the planar area increases by varying the shape of the topsurface from an approximately circle of the mask shape (Example 1) to anapproximately triangle of the substrate crystal shape (Example 4),resulting in increase in the reflected light from the inclined sidesurfaces.

Examples 5, 6

In Example 4, alignment structures of the protrusions according toExamples 5, 6, shown in FIGS. 15( a), 15(b) respectively, are formed.

In Example 4, the hexagonal arrangement of the mask is 30° rotated. Inother words, each of the two axis 11 a, 11 b are rotated 30° withrespect to the planar orientation of the substrate to form thestructure. The shape of the bottom surfaces 14 of the protrusions andthe constituent sides 16 thereof are formed dependant to the planarorientation of the substrate (A-axis direction indicated by arrows A inthe figures). The alignment is then varied accordingly to change in thedirections of the protrusions with respect to the periodic structure ofthe protrusions, i.e., the directions of vertex and constituent sides ofthe bottom surfaces.

In the periodic arrangements of the protrusions of Example 5 shown inFIG. 15( a) and Example 6 shown in FIG. 15( b), the constituent sides 16of the bottom surface of the protrusions are arranged intersecting withthe aligning direction in the axis directions thereof, and it isdifferent from that in Example 4 and Example 1, Specifically, in thealignments according to Examples 1, 4 shown in FIG. 1, one of theconstituent sides 16A, 16B, or 16C of the bottom surfaces isapproximately in parallel with the two axis directions 11 a, 11 b. Inthe example shown in FIG. 1, the constituent sides 16A are approximatelyin parallel with the aligning direction 11 a, and the constituent sides16C are approximately in parallel with the aligning direction 11 b. Onthe one hand, according to Examples 5, 6 shown in FIG. 15, all of theconstituent sides 16A, 16B, 16C are inclined with respect to the twoaligning directions 11 a, 11 b. In addition, the vertex direction of thebottom surface of the protrusions is inclined with respect to the twoalignment directions 11 a, 11 b, while it is in parallel in the exampleshown in FIG. 15.

When the constituent sides are disposed inclined with respect to thealigning directions, regions having a low density of the protrusions interms of reflection of light, which are the regions among the alignmentsin the above-described directions can be improved. In particular,according to Example 6 shown in FIG. 15( b), regions having a lowdensity are improved by alternately disposing the alignments ofprotrusions which are arranged adjacent in the alignment direction inthe regions among the alignments. In Example 5 shown in FIG. 15( a), thewidth of each row of the protrusions disposed in the alignment directionis larger than the interval of the rows. On the other hand, in Example 6shown in FIG. 15( b), the width of the rows B, C in the alignmentdirection 11 b are smaller than that of the interval of the rows. Thus,a part of the rows overlap each other in terms of the width of each rowof the protrusions.

As for the emission properties, the radiant flux of the light emittingelements of Examples 5, 6, and Example 4, obtained under the conditionsto be described below, is about 29.4 mW in Example 4, 29.7 mW in Example5, and 29.8 mW in Example 6. Thus, improvement in the region among therows of the protrusions having a low density described above has beenachieved. The radiation properties of a light emitting element having anemission wavelength of about 445 to 450 nm is evaluated by using a lightemitting device having a lamp shape, which is a resin mold type with 5mm in diameter. The protrusions of the light emitting elements of eachexamples are formed as such that the interval of the periodic structure,the distance between the median points of the bottom surface of adjacentprotrusions in Example 4 is formed in a similar manner as that inExample 1, the length of the sides of the triangle 11B is about 4.5 μmand the width of the top surface is about 1.5 μm in an example shown inFIG. 1. In Example 5, the interval of the periodic structures is about 4μm and the width of the top surface is about 1 μm, in Example 6, theinterval of the periodic structures is about 3 μm and the width of thetop surface is about 0.9 μm, and the width of the bottom surface of theprotrusions is about 2.8 μm in both examples.

INDUSTRIAL APPLICABILITY

The substrate of the present invention can be used not only for thelight emitting elements but also for other semiconductor elements toimprove the crystallinity of the semiconductor layer. Although thesubstrate of the present invention is illustrated with the protrusionsspaced apart each other, it is also applicable to the recesses ofsimilar configuration.

In the specification, the protrusions of the substrate are formed byprocessing the substrate, but the protrusions can also be formed on thesubstrate by providing protrusions with a light transmissive orreflective member, for example, by providing a film or a lighttransmissive film with a similar material as that of the protective filmor the mask. In this case, a material that is not decomposed during thegrowth of the semiconductor layer is used for the protrusion portion.

1. A method of manufacturing a substrate of a semiconductor lightemitting element comprising processes of: providing a mask on a firstmain surface of a substrate, forming a protrusion/recess structure onthe first main surface of the substrate by carrying out an etchingthrough the mask so as to form a plurality of protrusions each having atop surface and a bottom surface in different shapes and being spacedapart from each other, and forming a semiconductor substrate by growingsemiconductor on a surface of the recess/protrusion structure, whereinthe process of providing a mask comprises steps of forming a first maskwhich defines the shape of the bottom surface of protrusions, andforming a second mask which defines the shape of the top surface of theprotrusions on the first mask.
 2. The method of manufacturing asubstrate of a semiconductor light emitting element according to claim1, wherein the process of forming the protrusion/recess structurefurther comprises steps of: forming the bottom surface of each of theprotrusions wider than the top surface thereof in a cross section of thesubstrate, or forming the bottom surface of each of the protrusions soas to include the top surface in a top view of the substrate, andforming the bottom surface in an approximately polygonal shape, andforming the top surface in approximately circular shape or approximatelypolygonal shape with a larger number of constituent sides than thenumber of the constituent sides of the bottom surface.
 3. A method ofmanufacturing a substrate of a semiconductor light emitting elementcomprising processes of: providing a mask on a first main surface of asubstrate; forming a protrusion/recess structure on the first mainsurface of the substrate by carrying out an etching through the mask soas to form a plurality of protrusions each having a top surface and abottom surface in different shapes and being spaced apart from eachother; and forming a semiconductor substrate by growing semiconductor ona surface of the recess/protrusion structure, wherein the process offorming a recess/protrusion structure is carried out by wet etching andthe process includes a step of forming the shape of the bottom surfaceof the protrusions to include a crystal shape of substrate defined bythe wet etching.
 4. A method of manufacturing a substrate of asemiconductor light emitting element comprising processes of: providinga mask on a first main surface of a substrate; forming aprotrusion/recess structure on the first main surface of the substrateby carrying out an etching through the mask so as to form a plurality ofprotrusions each having a top surface and a bottom surface in differentshapes and being spaced apart from each other; and forming asemiconductor substrate by growing semiconductor on a surface of therecess/protrusion structure, wherein the process of providing a maskincludes forming the mask in an approximately circular shape, and theprocess of forming a recess/protrusion structure includes forming thebottom surface in a shape approximately a curve of constant width orReuleaux polygon.
 5. The method of manufacturing a substrate of asemiconductor light emitting element according to claim 1, wherein theprocess of forming a recess/protrusion structure includes a step ofperiodically arranging the protrusions in the first main surface of thesubstrate in a triangular, quadrangular, or hexagonal lattice.
 6. Themethod of manufacturing a substrate of a semiconductor light emittingelement according to claim 2, wherein the process of forming arecess/protrusion structure includes steps of aligning the protrusionsin two directions and forming a direction of the constituent sides ofthe bottom surface of the protrusions intersects with the directions ofthe aligning directions.
 7. The method of manufacturing a substrate of asemiconductor light emitting element according to claim 6, wherein theprocess of forming a recess/protrusion structure includes steps offorming an interval between adjacent alignments smaller than a width ofthe alignment, and aligning the protrusions in the directions as inclaim
 6. 8. A method of manufacturing a substrate of a semiconductorlight emitting element comprising processes of: providing a mask havinga shape of a curve of constant width on a first main surface of asubstrate, and forming a protrusion/recess structure having a pluralityof protrusions spaced apart each other on the first main surface of thesubstrate by carrying out a wet etching through the mask, so as to forma plurality of protrusions each having a bottom surface with a shapedifferent than that of the mask, which is approximately a curve ofconstant width or a Reuleaux polygon including a crystal shape of thesubstrate defined by the etching.
 9. The method of manufacturing asubstrate of a semiconductor light emitting element according to claim1, wherein the first mask and the second mask have different shapes. 10.The method of manufacturing a substrate of a semiconductor lightemitting element according to claim 1, wherein in the process of forminga protrusion/recess structure, the etching is carried out until thesecond mask is removed, to form the protrusions.
 11. The method ofmanufacturing a substrate of a semiconductor light emitting elementaccording to claim 9, wherein the substrate is a sapphire substrate, andwherein in the process of forming the protrusion/recess structure, wetetching is carried out using an etching solution of phosphoric acid orpyrophosphoric acid, a mixed acid of phosphoric or pyrophosphoric acidwith additional sulfuric acid, or solution of potassium hydroxide. 12.The method of manufacturing a substrate of a semiconductor lightemitting element according to claim 11, wherein the mask is made ofSiO₂.
 13. The method of manufacturing a substrate of a semiconductorlight emitting element according to claim 3, wherein in the process offorming the protrusion/recess structure, the top surface of each of theprotrusions is formed with an acuminate shape.
 14. The method ofmanufacturing a substrate of a semiconductor light emitting elementaccording to claim 3, wherein in the process of forming theprotrusion/recess structure, each of the protrusions is formed in apyramid shape.
 15. The method of manufacturing a substrate of asemiconductor light emitting element according to claim 3, wherein theprocess of providing a mask includes forming the mask in anapproximately circular shape, and the process of forming arecess/protrusion structure includes forming the bottom surface in ashape approximately a curve of constant width or Reuleaux polygon. 16.The method of manufacturing a substrate of a semiconductor lightemitting element according to claim 13, wherein the process of providinga mask includes forming the mask in an approximately circular shape, andthe process of forming a recess/protrusion structure includes formingthe bottom surface in a shape approximately a curve of constant width orReuleaux polygon.
 17. The method of manufacturing a substrate of asemiconductor light emitting element according to claim 14, wherein theprocess of providing a mask includes forming the mask in anapproximately circular shape, and the process of forming arecess/protrusion structure includes forming the bottom surface in ashape approximately a curve of constant width or Reuleaux polygon. 18.The method of manufacturing a substrate of a semiconductor lightemitting element according to claim 3, wherein the first main surface ofthe substrate is a C-plane of a sapphire substrate.
 19. The method ofmanufacturing a substrate of a semiconductor light emitting elementaccording to claim 3, wherein the process of forming a recess/protrusionstructure includes a step of periodically arranging the protrusions inthe first main surface of the substrate in a triangular, quadrangular,or hexagonal lattice.
 20. The method of manufacturing a substrate of asemiconductor light emitting element according to claim 3, wherein theprocess of forming the protrusion/recess structure further comprisessteps of: forming the bottom surface of each of the protrusions widerthan the top surface thereof in a cross section of the substrate, orforming the bottom surface of each of the protrusions so as to includethe top surface in a top view of the substrate, and forming the bottomsurface in an approximately polygonal shape, and forming the top surfacein approximately circular shape or approximately polygonal shape with alarger number of constituent sides than the number of the constituentsides of the bottom surface.
 21. The method of manufacturing a substrateof a semiconductor light emitting element according to claim 20, whereinthe process of forming a recess/protrusion structure includes steps ofaligning the protrusions in two directions and forming a direction ofthe constituent sides of the bottom surface of the protrusionsintersects with the directions of the aligning directions.
 22. Themethod of manufacturing a substrate of a semiconductor light emittingelement according to claim 21, wherein the process of forming arecess/protrusion structure includes steps of forming an intervalbetween adjacent alignments smaller than a width of the alignment, andaligning the protrusions in the directions as in claim 21.